The course

One path, in order, from no Java at all to a full graded design round. Work top to bottom. Every chapter says what you need before it and what to read next.

Start here → 1.1 A class, an object, and main()the first chapter

33 of 33 chapters written. Reading counts toward nothing — the graded half is in the app.

Java, from nothing

No Java assumed. By the end of this part you can read and write the Java that every later chapter uses, and you will have compiled and run every example yourself.

1.1 · A class, an object, and main()25 min 1.2 · Fields, methods, and constructors30 min 1.3 · References, null, and what equals really compares30 min 1.4 · Inheritance and polymorphism: extends, super, overriding, and dynamic dispatch45 min 1.5 · Interfaces: naming a contract30 min 1.6 · Abstract classes, and when an interface is better25 min 1.7 · The three collections you need: List, Map, Set35 min 1.8 · Generics, as far as you actually need them30 min 1.9 · Exceptions, and choosing what to throw30 min 1.10 · enum and record: the two types you will reach for most30 min

Objects that hold their shape

The five SOLID principles and the habits underneath them. Each one is taught the same way: working code, a new requirement, the cost that forces a change, then the name of the principle.

2.1 · Encapsulation: deciding who can change your data30 min 2.2 · Immutability, and the bugs it deletes30 min 2.3 · Composition over inheritance30 min 2.4 · Single responsibility, and how to test for it30 min 2.5 · Open for extension, closed for modification30 min 2.6 · Liskov substitution: keeping a promise a caller relies on30 min 2.7 · Interface segregation: the smallest useful contract25 min 2.8 · Dependency inversion, and injecting the clock30 min

Patterns you will actually be asked for

One pattern per chapter, in the order they turn up in interviews. Each chapter names the pattern only after you have felt why it exists, and says plainly when using it would be a mistake.

3.1 · Strategy: behaviour you can swap30 min 3.2 · Factory: construction kept away from use30 min 3.3 · Builder: too many constructor arguments25 min 3.4 · Observer: telling other objects something happened30 min 3.5 · State: a transition table you can read35 min 3.6 · Decorator and Chain of Responsibility35 min 3.7 · Template method: a fixed skeleton with holes25 min 3.8 · Adapter and Facade: making other people's code fit30 min 3.9 · Singleton, and why interviewers hope you avoid it25 min 3.10 · Composite and Iterator: trees and traversal30 min

Designing under pressure

Everything above was preparation. This part is the graded half: the eight phases, the 20 problems with measured curveballs, and the 48 reference lessons you are now equipped to read.

4.1 · Reading a vague prompt without panicking30 min 4.2 · Saying what you will not build25 min 4.3 · Drawing a class diagram fast30 min 4.4 · Two threads, one object40 min 4.5 · Your first full round, start to finish45 min

After the course

High-level design, algorithms, databases and the rest of the interview loop are not taught here. This page says so plainly, and where to go for each.

What to learn after this course15 min